#include<iostream> 
#include<stdio.h>
#include<string.h>
#include<cmath>
//#include<conio.h>
using namespace std;
int main()
{
    int n;
    char ch1[50],ch2[50],ch3[50];
    char c;
    while(scanf("%d",&n)!=EOF)
    {
         int sum1=0;
         //zzz->first
         cin>>ch1>>ch2>>ch3;
         for(int i=0;i<n;i++)
          if (ch2[i]==ch3[i]&&ch1[i]!=ch2[i]) sum1+=2; 
          else if (ch1[i]!=ch2[i]||ch1[i]!=ch3[i]) sum1++;
         cout<<sum1<<endl;
    
    }
    //system("pause");
    return 0;
}
